We've offered up a number of DIY products to make your flash photography look a bit better, but Flickr user synthetic_meat managed to find another one in a box of candy. He refolded that box, which had a silver lining, to create a mirrored popup flash bouncer for his camera:
I recently had some delectable snacks "Schaumküsse". They were in a nice cardboard box with a mirrored silver lining (haha!).
This gave me an idea -- I had to use it as a lighting accessory! After a bit of cutting, scoring and folding, and a few paper clips, I came up with this foldable lightscoop-clone. It bounces the popup flash onto the ceiling or, if the camera is held in portrait orientation, the wall.
This DIY trick, which you can see in its various stages in the image above, is modelled after a product called the Lightscoop and these instructions. Basically, all you need to do is have a reflective surface facing the flash at a 45° angle. This will bounce the light to the ceiling (or to the wall) and you'll get a flash-based image that's far more appealing than the washed-out pictures a flash affords you when pointed head-on.